This invention is generally directed to an overcoated photoreceptor device, and more specifically, to an overcoated photoreceptor device containing an electron trapping layer and a hole trapping layer, and a method of imaging utilizing such a device.
The formation and development of images on the imaging surfaces of photoconductive materials by electrostatic means is well known, one of the most widely used processes being xerography as described in U.S. Pat. No. 2,297,691. Numerous different types of photoreceptors can be used in the electrophotographic process, such photoreceptors including inorganic materials, organic materials and mixtures thereof. Photoreceptors are known wherein the charge generation and charge carrier transport functions are accomplished by discrete contiguous layers. Also known are photoreceptors which include an overcoating layer of an electrically insulating polymeric material, and in conjunction with this overcoated type photoreceptor there have been proposed a number of imaging methods. However, the art of electrophotography and more specifically, xerography, continues to advance and more strigent demands need to be met by the copying apparatus in order to increase performance standards, and obtain higher quality images. Also, photoreceptor devices are needed which contain overcoatings that function as a protectent for the photoreceptor.
In one known process using overcoated photoreceptor devices there is employed a non-ambipolar photoconductor wherein charge carriers are injected from the substrate into the photoconductor surface. In such a system in order to obtain high quality images the injecting electrode must satisfy the requirements that it injects carriers efficiently and uniformly into the photoconductor. A method for utilizing organic overcoated photoreceptor devices has been recently discovered and is described in copending application, U.S. Ser. No. 881,262, filed on Feb. 24, 1978 on Electrophotographic Imaging Method, Simpei Tutihasi, Inventor. In the method described in this application, there is utilized an imaging member comprising a substrate, a layer or charge carrier injecting electrode material, a layer of a charge carrier transport material, a layer of a photoconductive charge carrier generating material and an electrically insulating overcoating layer. In one embodiment of operation, the member is charged a first time with electrostatic charges of a first polarity, charged a second time with electrostatic charges of a polarity opposite to the first polarity in order to substantially neutralize the charges residing on the electrically insulating surface of the member and exposed to an imagewise pattern of activating electromagnetic radiation whereby an electrostatic latent image is formed. The electrostatic latent image may then be developed to form a visible image which can be transferred to a receiving member. Subsequently, the imaging member may be reused to form additional reproductions after the erasure and cleaning steps have been accomplished. The actual operation of this member is best illustrated by referring to FIGS. 2A-2C of the present application. While these devices function properly and adequately, there continues to be a need for improved photoreceptor devices which contain a hole trapping layer, and an electron trapping layer, thus allowing for the production of images of high quality over extended periods of time. Also there continues to be a need for overcoated photoreceptors, particularly inorganic overcoated photoreceptors, wherein electrons are trapped at the substrate, and holes or positive charges are trapped at the generating layer overcoating layer interface, which photoreceptor is very efficient and economical to manufacture, and which can be utilized for causing the formation of images in electrophotographic imaging systems.